I have backpacked through columbia and ecuador with the scuba gear for a couple of months. Busses, trains, ferries etc. Also belize to mexico.
I carry a 55L pack (maximum carryon) and a 30L that can fit underseat(personal item). For south america it is open water non-tech diving.
55L gets the bpw, regs, fins, 5mm, mask, computers, dsmb etc. BPW is custom designed to be light weight (nylon plate, aluminum/nylon hardware) but I splurge on deep 6 eddy fins.
30L is all personal items for 2 months. Much easier to buy clothes and personal items then scuba gear while traveling.
For mexico the weight goes up, but the sidemount setup, sidemount regs, lights, reels all fit in the 55L. The helmet goes in the 30L. If I pull the 5mm out, I can fit the trilam drysuit into the 55L with the sidemount harness, fins, but have to dump the helmet and most of the clothes as regs, mask, computers go in the 30L. I have to wear the chuck taylors as my main shoes which is not my favorite for trekking.
The drysuit and rebreather have a pelican case (love the pelican air 1626 that either flies with me or goes DHL)
I know that my trips are going to be ~8 dives a week. (60 dives in 2 months) This makes it worth it to me to have my own gear that I can service. I think you should decide what kind of trip it is (Is it backpacking to different diving destinations) or backpacking with a bit of diving along the way.